The preesent invention relates to rotary wing aircraft, and in particular to a jet nozzle driven rotary wing aircraft which has means for folding at least one of the rotor blades about the rotor hub of the rotor assembly.
In rotary wing aircraft, such as helicopters, it often times is desirable to be able to fold one or more of the rotor blades to an inoperative or storing position so as to reduce the overall lateral dimensions of the craft. This is desirable for storing the craft in hangers, or during air or sea transport.
With conventional helicopters, the blades may be secured to the hub of the rotor by various forms of mechanical hinge means and the blades are interconnected by stay wires or the like for maintaining the relative position of the blades in their normal, radially outward, unfolded operative positions.
However, the development of high performance lightweight gas turbines has made it increasingly feasible to power the rotor assembly of a helicopter by ducting compressed air and/or the turbine gases directly to jet nozzles located at the rotor blade tips. This technique of rotor drive obviously eliminates the need for heavy torque transmitting members from the engine to the rotor blades and, additionally, the blades have a tendency to establish equilibrium by the action of the medium passing through the interior of the blades, along with centrifugal forces. With the rotor assembly being driven by the reactive force of a jet stream of air passing through the interior of the rotor blades, any folding means must not obstruct the free flow of the air through the blades, and the blades must be maintained substantially air impervious to the atmosphere without interferring with the movability of the folding means.
A principal object, therefore, of the present invention is to provide in a rotary wing aircraft, a new and improved means for folding the rotor blades relative to the rotor hub of the rotor assembly.
In the exemplary embodiment of the invention, a rotary wing aircraft is shown to include a fuselage, air compressor means within the fuselage, and a jet nozzle driven rotor assembly situated over the fuselage and having a rotor axis about which the assembly rotates. The rotor assembly includes a generally hollow rotor hub and a plurality of generally hollow jet nozzle driven rotor blades extending radially outwardly of the rotor hub. The hub defines an air conduit means to the rotor blades. Means is provided for folding at least one of the rotor blades in a radial plane relative to the rotor hub.
The folding means includes a section of the rotor blade comprising flexible air conduit means. Releasable stabilizing means is disposed between the rotor hub and an outboard portion of the rotor blade beyond the flexible air conduit section, whereby the stabilizing means may be released and the blade folded in its radial plane with the flexible air conduit section acting as a hinge. Preferrably, the flexible air conduit section is of sufficient length to permit the rotor blade to be folded in a full 180.degree. from its normal, radially outward, unfolded operative position.
In the embodiment of the invention shown herein, the stabilizing means includes a droop stop which prevents the rotor blade from tilting below a predetermined angle relative to the rotor hub. The droop stop is elongated and extends between the outboard portion of the rotor blade and a base portion of the rotor hub. In the exemplary embodiment of the invention, the droop stop is fixed at one end thereof to the outboard portion of the rotor blade, and is in free abutment at the other end thereof with the base portion of the rotor hub. A brace member is releasably connected at one end thereof to the rotor hub at a point spaced from said base portion thereof, and is slidably connected to the droop stop intermediate the ends thereof. Stop limit means is provided on the droop stop to limit the sliding movement of the brace member therealong.
Torsion means is provided to maintain the rotor blade in its radial plane notwithstanding the release of the stabilizing means for folding the blade.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.